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On April 17, 2009, CDC determined that two cases of febrile respiratory illness occurring in children who resided in adjacent counties in southern California were caused by infection with a swine influenza A (H1N1) virus. The viruses from the two cases are closely related genetically, resistant to amantadine and rimantadine, and contain a unique combination of gene segments that previously has not been reported among swine or human influenza viruses in the United States or elsewhere. Neither child had contact with pigs; the source of the infection is unknown. Investigations to identify the source of infection and to determine whether additional persons have been ill from infection with similar swine influenza viruses are ongoing. This report briefly describes the two cases and the investigations currently under way. Although this is not a new subtype of influenza A in humans, concern exists that this new strain of swine influenza A (H1N1) is substantially different from human influenza A (H1N1) viruses, that a large proportion of the population might be susceptible to infection, and that the seasonal influenza vaccine H1N1 strain might not provide protection. The lack of known exposure to pigs in the two cases increases the possibility that human-to-human transmission of this new influenza virus has occurred. Clinicians should consider animal as well as seasonal influenza virus infections in their differential diagnosis of patients who have febrile respiratory illness and who 1) live in San Diego and Imperial counties or 2) traveled to these counties or were in contact with ill persons from these counties in the 7 days preceding their illness onset, or 3) had recent exposure to pigs. Clinicians who suspect swine influenza virus infections in a patient should obtain a respiratory specimen and contact their state or local health department to facilitate testing at a state public health laboratory.

Case Reports

Patient A. On April 13, 2009, CDC was notified of a case of respiratory illness in a boy aged 10 years who lives in San Diego County, California. The patient had onset of fever, cough, and vomiting on March 30, 2009. He was taken to an outpatient clinic, and a nasopharyngeal swab was collected for testing as part of a clinical study. The boy received symptomatic treatment, and all his symptoms resolved uneventfully within approximately 1 week. The child had not received influenza vaccine during this influenza season. Initial testing at the clinic using an investigational diagnostic device identified an influenza A virus, but the test was negative for human influenza subtypes H1N1, H3N2, and H5N1. The San Diego County Health Department was notified, and per protocol, the specimen was sent for further confirmatory testing to reference laboratories, where the sample was verified to be an unsubtypable influenza A strain. On April 14, 2009, CDC received clinical specimens and determined that the virus was swine influenza A (H1N1). The boy and his family reported that the child had had no exposure to pigs. Investigation of potential animal exposures among the boy's contacts is continuing. The patient's mother had respiratory symptoms without fever in the first few days of April 2009, and a brother aged 8 years had a respiratory illness 2 weeks before illness onset in the patient and had a second illness with cough, fever, and rhinorrhea on April 11, 2009. However, no respiratory specimens were collected from either the mother or brother during their acute illnesses. Public health officials are conducting case and contact investigations to determine whether illness has occurred among other relatives and contacts in California, and during the family's travel to Texas on April 3, 2009.

Patient B.

CDC received an influenza specimen on April 17, 2009, that had been forwarded as an unsubtypable influenza A virus from the Naval Health Research Center in San Diego, California. CDC identified this specimen as a swine influenza A (H1N1) virus on April 17, 2009, and notified the California Department of Public Health. The source of the specimen, patient B, is a girl aged 9 years who resides in Imperial County, California, adjacent to San Diego County. On March 28, 2009, she had onset of cough and fever (104.3&#176;F [40.2&#176;C]). She was taken to an outpatient facility that was participating in an influenza surveillance project, treated with amoxicillin/clavulanate potassium and an antihistamine, and has since recovered uneventfully. The child had not received influenza vaccine during this influenza season. The patient and her parents reported no exposure to pigs, although the girl did attend an agricultural fair where pigs were exhibited approximately 4 weeks before illness onset. She reported that she did not see pigs at the fair and went only to the amusement section of the fair. The Imperial County Public Health Department and the California Department of Public Health are now conducting an investigation to determine possible sources of infection and to identify any additional human cases. The patient's brother aged 13 years had influenza-like symptoms on April 1, 2009, and a male cousin aged 13 years living in the home had influenza-like symptoms on March 25, 2009, 3 days before onset of the patient's symptoms. The brother and cousin were not tested for influenza at the time of their illnesses.

Epidemiologic and Laboratory Investigations

As of April 21, 2009, no epidemiologic link between patients A and B had been identified, and no additional cases of infection with the identified strain of swine influenza A (H1N1) had been identified. Surveillance data from Imperial and San Diego counties, and from California overall, showed declining influenza activity at the time of the two patients' illnesses. Case and contact investigations by the county and state departments of health in California and Texas are ongoing. Enhanced surveillance for possible additional cases is being implemented in the area.

Preliminary genetic characterization of the influenza viruses has identified them as swine influenza A (H1N1) viruses. The viruses are similar to each other, and the majority of their genes, including the hemagglutinin (HA) gene, are similar to those of swine influenza viruses that have circulated among U.S. pigs since approximately 1999; however, two genes coding for the neuraminidase (NA) and matrix (M) proteins are similar to corresponding genes of swine influenza viruses of the Eurasian lineage (1). This particular genetic combination of swine influenza virus segments has not been recognized previously among swine or human isolates in the United States, or elsewhere based on analyses of influenza genomic sequences available on GenBank.* Viruses with this combination of genes are not known to be circulating among swine in the United States; however, no formal national surveillance system exists to determine what viruses are prevalent in the U.S. swine population. Recent collaboration between the U.S. Department of Agriculture and CDC has led to development of a pilot swine influenza virus surveillance program to better understand the epidemiology and ecology of swine influenza virus infections in swine and humans.

The viruses in these two patients demonstrate antiviral resistance to amantadine and rimantadine, and testing to determine susceptibility to the neuraminidase inhibitor drugs oseltamivir and zanamivir is under way. Because these viruses carry a unique combination of genes, no information currently is available regarding the efficiency of transmission in swine or in humans. Investigations to understand transmission of this virus are ongoing.

In the past, CDC has received reports of approximately one human swine influenza virus infection every 1--2 years in the United States (2,3). However, during December 2005--January 2009, 12 cases of human infection with swine influenza were reported; five of these 12 cases occurred in patients who had direct exposure to pigs, six in patients reported being near pigs, and the exposure in one case was unknown (1,4,5). In the United States, novel influenza A virus infections in humans, including swine influenza infections, have been nationally notifiable conditions since 2007. The recent increased reporting might be, in part, a result of increased influenza testing capabilities in public health laboratories, but genetic changes in swine influenza viruses and other factors also might be a factor (1,4,5). Although the vast majority of human infections with animal influenza viruses do not result in human-to-human transmission (2,3), each case should be fully investigated to be certain that such viruses are not spreading among humans and to limit further exposure of humans to infected animals, if infected animals are identified. Such investigations should include close collaboration between state and local public health officials with animal health officials.

The lack of known exposure to pigs in the two cases described in this report increases the possibility that human-to-human transmission of this new influenza virus has occurred. Clinicians should consider animal as well as seasonal influenza virus infections in the differential diagnosis of patients with febrile respiratory illness who live in San Diego and Imperial counties or have traveled to these areas or been in contact with ill persons from these areas in the 7 days before their illness onset. In addition, clinicians should consider animal influenza infections among persons with febrile respiratory illness who have been near pigs, such as attending fairs or other places where pigs might be displayed. Clinicians who suspect swine influenza virus infections in humans should obtain a nasopharyngeal swab from the patient, place the swab in a viral transport medium, and contact their state or local health department to facilitate transport and timely diagnosis at a state public health laboratory. CDC requests that state public health laboratories send all influenza A specimens that cannot be subtyped to the CDC, Influenza Division, Virus Surveillance and Diagnostics Branch Laboratory.

Vincent AL, Swenson SL, Lager KM, Gauger PC, Loiacono C, Zhang Y. Characterization of an influenza A virus isolated from pigs during an outbreak of respiratory disease in swine and people during a county fair in the United States. Vet Microbiol 2009;online publication ahead of print.

On April 21, 2009, CDC reported that two recent cases of febrile respiratory illness in children in southern California had been caused by infection with genetically similar swine influenza A (H1N1) viruses. The viruses contained a unique combination of gene segments that had not been reported previously among swine or human influenza viruses in the United States or elsewhere (1). Neither child had known contact with pigs, resulting in concern that human-to-human transmission might have occurred. The seasonal influenza vaccine H1N1 strain is thought to be unlikely to provide protection. This report updates the status of the ongoing investigation and provides preliminary details about six additional persons infected by the same strain of swine influenza A (H1N1) virus identified in the previous cases, as of April 24. The six additional cases were reported in San Diego County, California (three cases), Imperial County, California (one case), and Guadalupe County, Texas (two cases). CDC, the California Department of Public Health, and the Texas Department of Health and Human Services are conducting case investigations, monitoring for illness in contacts of the eight patients, and enhancing surveillance to determine the extent of spread of the virus. CDC continues to recommend that any influenza A viruses that cannot be subtyped be sent promptly for testing to CDC. In addition, swine influenza A (H1N1) viruses of the same strain as those in the U.S. patients have been confirmed by CDC among specimens from patients in Mexico. Clinicians should consider swine influenza as well as seasonal influenza virus infections in the differential diagnosis for patients who have febrile respiratory illness and who 1) live in San Diego and Imperial counties, California, or Guadalupe County, Texas, or traveled to these counties or 2) who traveled recently to Mexico or were in contact with persons who had febrile respiratory illness and were in one of the three U.S. counties or Mexico during the 7 days preceding their illness onset.

Case Reports

San Diego County, California. On April 9, an adolescent girl aged 16 years and her father aged 54 years went to a San Diego County clinic with acute respiratory illness. The youth had onset of illness on April 5. Her symptoms included fever, cough, headache, and rhinorrhea. The father had onset of illness on April 6 with symptoms that included fever, cough, and rhinorrhea. Both had self-limited illnesses and have recovered. The father had received seasonal influenza vaccine in October 2008; the daughter was unvaccinated. Respiratory specimens were obtained from both, tested in the San Diego County Health Department Laboratory, and found to be positive for influenza A using reverse transcription--polymerase chain reaction (RT-PCR), but could not be further subtyped. Two household contacts of the patients have reported recent mild acute respiratory illnesses; specimens have been collected from these household members for testing. One additional case, in a child residing in San Diego County, was identified on April 24; epidemiologic details regarding this case are pending.

Imperial County, California. A woman aged 41 years with an autoimmune illness who resided in Imperial County developed fever, headache, sore throat, diarrhea, vomiting, and myalgias on April 12. She was hospitalized on April 15. She recovered and was discharged on April 22. A respiratory specimen obtained April 16 was found to be influenza A positive by RT-PCR at the San Diego Country Health Department Laboratory, but could not be further subtyped. The woman had not been vaccinated against seasonal influenza viruses during the 2008--09 season. Three household contacts of the woman reported no recent respiratory illness.

Guadalupe County, Texas. Two adolescent boys aged 16 years who resided in Guadalupe County near San Antonio were tested for influenza and found to be positive for influenza A on April 15. The youths had become ill with acute respiratory symptoms on April 10 and April 14, respectively, and both had gone to an outpatient clinic for evaluation on April 15. Identification and tracking of the youths' contacts is under way.

Five of the new cases were identified through diagnostic specimens collected by the health-care facility in which the patients were examined, based on clinical suspicion of influenza; information regarding the sixth case is pending. The positive specimens were sent to public health laboratories for further evaluation as part of routine influenza surveillance in the three counties.

Outbreaks in Mexico

Mexican public health authorities have reported increased levels of respiratory disease, including reports of severe pneumonia cases and deaths, in recent weeks. Most reported disease and outbreaks are reported from central Mexico, but outbreaks and severe respiratory disease cases also have been reported from states along the U.S.-Mexico border. Testing of specimens collected from persons with respiratory disease in Mexico by the CDC laboratory has identified the same strain of swine influenza A (H1N1) as identified in the U.S. cases. However, no clear data are available to assess the link between the increased disease reports in Mexico and the confirmation of swine influenza in a small number of specimens. CDC is assisting public health authorities in Mexico in testing additional specimens and providing epidemiologic support. None of the U.S. patients traveled to Mexico within 7 days of the onset of their illness.

Epidemiologic and Laboratory Investigations

As of April 24, epidemiologic links identified among the new cases included 1) the household of the father and daughter in San Diego County, and 2) the school attended by the two youths in Guadalupe County. As of April 24, no epidemiologic link between the Texas cases and the California cases had been identified, nor between the three new California cases and the two cases previously reported. No recent exposure to pigs has been identified for any of the seven patients. Close contacts of all patients are being investigated to determine whether person-to-person spread has occurred.

Enhanced surveillance for additional cases is ongoing in California and in Texas. Clinicians have been advised to test patients who visit a clinic or hospital with febrile respiratory illness for influenza. Positive samples should be sent to public health laboratories for further characterization. Seasonal influenza activity continues to decline in the United States, including in Texas and California, but remains a cause of influenza-like illness in both areas.

Viruses from six of the eight patients have been tested for resistance to antiviral medications. All six have been found resistant to amantadine and rimantidine but sensitive to zanamivir and oseltamivir.

Reported by: San Diego County Health and Human Svcs; Imperial County Public Health Dept; California Dept of Public Health. Dallas County Health and Human Svcs; Texas Dept of State Health Svcs. Naval Health Research Center; Navy Medical Center, San Diego, California. Animal and Plant Health Inspection Svc, US Dept of Agriculture. Div of Global Migration and Quarantine, National Center for Preparedness, Detection, and Control of Infectious Diseases; National Center for Zoonotic, Vector-Borne, and Enteric Diseases; Influenza Div, National Center for Infectious and Respiratory Diseases, CDC.Editorial Note:

In the United States, novel influenza A virus infections in humans, including swine influenza A (H1N1) infections, have been nationally notifiable conditions since 2007. Recent pandemic influenza preparedness activities have greatly increased the capacity of public health laboratories in the United States to perform RT-PCR for influenza and to subtype influenza A viruses they receive from their routine surveillance, enhancing the ability of U.S. laboratories to identify novel influenza A virus infections. Before the cases described in this ongoing investigation, recent cases of swine influenza in humans reported to CDC occurred in persons who either had exposure to pigs or to a family member with exposure to pigs. Transmission of swine influenza viruses between persons with no pig exposure has been described previously, but that transmission has been limited (2,3). The lack of a known history of pig exposure for any of the patients in the current cases indicates that they acquired infection through contact with other infected persons.

The spectrum of illness in the current cases is not yet fully defined. In the eight cases identified to date, six patients had self-limited illnesses and were treated as outpatients. One patient was hospitalized. Previous reports of swine influenza, although in strains different from the one identified in the current cases, mostly included mild upper respiratory illness; but severe lower respiratory illness and death also have been reported (2,3).

The extent of spread of the strain of swine influenza virus in this investigation is not known. Ongoing investigations by California and Texas authorities of the two previously reported patients, a boy aged 10 years and a girl aged 9 years, include identification of persons in close contact with the children during the period when they were likely infectious (defined as from 1 day before symptom onset to 7 days after symptom onset). These contacts have included household members, extended family members, clinic staff members who cared for the children, and persons in close contact with the boy during his travel to Texas on April 3. Respiratory specimens are being collected from contacts found to have ongoing illness. In addition, enhanced surveillance for possible cases is under way in clinics and hospitals in the areas where the patients reside. Similar investigations and enhanced surveillance are now under way in the additional six cases.

Clinicians should consider swine influenza infection in the differential diagnosis of patients with febrile respiratory illness and who 1) live in San Diego and Imperial counties, California, or Guadalupe County, Texas, or traveled to these counties or 2) who traveled recently to Mexico or were in contact with persons who had febrile respiratory illness and were in one of the three U.S. counties or Mexico during the 7 days preceding their illness onset. Any unusual clusters of febrile respiratory illness elsewhere in the United States also should be investigated.

Patients who meet these criteria should be tested for influenza, and specimens positive for influenza should be sent to public health laboratories for further characterization. Clinicians who suspect swine influenza virus infections in humans should obtain a nasopharyngeal swab from the patient, place the swab in a viral transport medium, refrigerate the specimen, and then contact their state or local health department to facilitate transport and timely diagnosis at a state public health laboratory. CDC requests that state public health laboratories promptly send all influenza A specimens that cannot be subtyped to the CDC, Influenza Division, Virus Surveillance and Diagnostics Branch Laboratory. As a precautionary step, CDC is working with other partners to develop a vaccine seed strain specific to these recent swine influenza viruses in humans.
As always, persons with febrile respiratory illness should stay home from work or school to avoid spreading infections (including influenza and other respiratory illnesses) to others in their communities. In addition, frequent hand washing can lessen the spread of respiratory illness (5). Interim guidance on infection control, treatment, and chemoprophylaxis for swine influenza is available at http://www.cdc.gov/flu/swine/recommendations.htm. Additional information about swine influenza is available at http://www.cdc.gov/flu/swine/index.htm.

Comment

CDC has released sequences for all 8 gene segments from H1N1 from San Diego case (10M). The mixture is not very unusal, except for previous description of North American HA and Eurasian NA and M. Other genes are

Comment

So this strain appears to be more transmissable than other swine/human flus because.... ???

.

Although HA is like other North American swine H1's, it still has quite a few differences (as does NA). In addition to reassortment, swine does a lot of recombining. But this is just the first wave. Now that it is established in the human population, it will pick up more human flu polymorphisms. Wave 2 will be the real killer.

Perhaps the maps should be a separate thread so that we can track locations where people may have vacationed in the last while, with a fancy orange button at the top (wonderful site addition, IMO!!).

Further, if possible contacts need to be considered (e.g.. advising people who may have visited these locations to work at home for awhile) for what period should we be concerned about - the last week, 2 weeks, month?

<!-- content area --> <!-- body area --> Update: Infections With a Swine-Origin Influenza A (H1N1) Virus --- United States and Other Countries, April 28, 2009

Since April 21, 2009, CDC has reported cases of respiratory infection with a swine-origin influenza A (H1N1) virus (S-OIV) transmitted through human-to-human contact (1,2). This report updates cases identified in U.S. states and highlights certain control measures taken by CDC. As of April 28, the total number of confirmed cases of S-OIV infection in the United States had increased to 64, with cases in California (10 cases), Kansas (two), New York (45), Ohio (one), and Texas (six). CDC and state and local health departments are investigating all reported U.S. cases to ascertain the clinical features and epidemiologic characteristics. On April 27, CDC distributed an updated case definition for infection with S-OIV (Box). Of the 47 patients reported to CDC with known ages, the median age was 16 years (range: 3--81 years), and 38 (81%) were aged <18 years; 51% of cases were in males. Of the 25 cases with known dates of illness onset, onset ranged from March 28 to April 25 (Figure). To date, no deaths have been reported among U.S. cases, but five patients are known to have been hospitalized. Of 14 patients with known travel histories, three had traveled to Mexico; 40 of 47 patients (85%) have not been linked to travel or to another confirmed case. Information is being compiled regarding vaccination status of infected patients, but is not yet available. According to the World Health Organization (WHO), as of April 27, a total of 26 confirmed cases of S-OIV infection had been reported by Mexican authorities. Canada has reported six cases and Spain has reported one case.* Emergency Use AuthorizationsIf an emerging public health threat is identified for which no licensed or approved product exists, the Project BioShield Act of 2004 authorizes the Food and Drug Administration (FDA) commissioner to issue an Emergency Use Authorization (EUA) so that promising countermeasures can be disseminated quickly for the protection and safety of the U.S. population (3). In response to the current public health emergency involving swine-origin influenza, FDA issued four EUAs on April 27 to allow emergency use of

oseltamivir (Tamiflu) and zanamivir (Relenza) for the treatment and prophylaxis of influenza (two EUAs),

disposable N95 respirators for use by the general public, and

the rRT-PCR Swine Flu Panel for diagnosis.

Oseltamivir is FDA-approved for treatment and prevention of influenza in adults and children aged ≥1 year. Zanamivir is FDA-approved for treatment of influenza in adults and children aged ≥7 years who have been symptomatic for <2 days, and for prevention of influenza in adults and children aged ≥5 years. The EUA allows the use of oseltamivir for treatment of influenza in children aged <1 year and prevention of influenza in children aged 3 months--1 year. Additionally, traditional prescribing and dispensing requirements might not be met. Under the scope and conditions of current EUAs, mass dispensing of both antiviral medications will be allowed per state and/or local public health authority. FDA has authorized use of certain N95 respirators to help reduce wearer exposure to pathogenic biological airborne particulates during a public health emergency involving S-OIV. On April 27, CDC published guidelines for the use of N95 respirators. For example, respirators should be considered for use by persons for whom close contact with an infectious person is unavoidable. This can include selected individuals who must care for a sick person (e.g., family member with a respiratory infection) at home. Additional information is available at http://www.cdc.gov/swineflu/masks.htm. Currently, no FDA-cleared tests specifically for the S-OIV strain exist in the United States or elsewhere. For this purpose and to meet the significant increase in demand for influenza testing throughout the country, CDC has developed the rRT-PCR Swine Flu Panel to expand and maintain the operational capabilities of public health or other qualified laboratories by providing a detection tool for the presumptive presence of S-OIV. Control Measures at Ports of Entry and Travel Warning for MexicoCDC, in collaboration with industry and federal partners, is continuing to conduct routine illness detection at ports of entry with heightened awareness for travelers who might be infected with S-OIV. During April 19--27, 15 cases of illness in travelers entering the United States from Mexico that were clinically consistent with S-OIV infection were detected. Of these 15 cases, two were laboratory confirmed as swine-origin influenza A (H1N1). Nine travelers remain in isolation pending completion of evaluation, and four travelers were released to complete travel after influenza virus infection was ruled out.WHO has declared a Public Health Emergency of International Concern. As part of its responsibilities under the International Health Regulations, CDC is prepared to implement additional screening measures for international flights, if deemed necessary, to prevent exportation of S-OIV. In addition, CDC in collaboration with the U.S. Department of Homeland Security, is distributing travelers health alert notices to all persons traveling to countries with confirmed cases of S-OIV infection.CDC has recommended that U.S. travelers avoid nonessential travel to Mexico (http://wwwn.cdc.gov/travel/contentSwineFluMexico.aspx). However, CDC might revise its travel guidance as the outbreak in Mexico evolves and is characterized more completely. Travelers who cannot delay travel to Mexico should visit http://[URL="file://cdc/project/NCHM_OD_MMWR/Dispatch/MM%2058%20series%20%282009%29/Dispatch%2004-28-09%20pm/Dispatch%2004-28-09%20B%20docs%20%26%20figs/www.cdc.gov/travel"]www.cdc.gov/travel[/url] and follow the posted recommendations to reduce their risk for infection. Nonpharmaceutical Community MitigationCDC has issued interim guidance for nonpharmaceutical community mitigation efforts in response to human infections with S-OIV (http://www.cdc.gov/swineflu/mitigation.htm). Current recommendations for isolation of patients with cases of S-OIV, household contacts, school dismissal, and other social distancing interventions also are available at http://www.cdc.gov/swineflu/mitigation.htm and will be updated as the situation evolves. Reported by: Strategic Science and Program Unit, Coordinating Center for Infectious Diseases; Div of Global Migration and Quarantine, National Center for Preparedness, Detection, and Control of Infectious Diseases; Influenza Div, National Center for Immunization and Respiratory Diseases, CDC Influenza Emergency Response Team, CDC.References

The following case definitions are for the purposes of investigations of suspected, probable, and confirmed cases of swine-origin influenza A (H1N1) infection.Case Definitions for Infection with Swine-Origin Influenza A (H1N1) VirusA confirmed case of swine-origin influenza A (H1N1) virus infection is defined as an acute febrile respiratory illness in a person and laboratory-confirmed swine-origin influenza A (H1N1) virus infection at CDC by either of the following tests: 1) real-time reverse transcrition--polymerase chain
reaction (rRT-PCR), or 2) viral culture. A probable case of swine-origin influenza A (H1N1) virus infection is defined as acute febrile respiratory illness in a person who is positive for influenza A, but negative for H1 and H3 by influenza rRT-PCR. A suspected case of swine-origin influenza A (H1N1) virus infection is defined as acute febrile respiratory illness in a person  with onset within 7 days of close contact with a person who has a confirmed case of swine-origin influenza A (H1N1) virus infection, or with onset within 7 days of travel to a community, either within the United States or internationally, which has one or more confirmed swine-origin influenza A (H1N1) cases, or who resides in a community in which one or more confirmed swine-origin influenza cases have occurred.

FIGURE. Confirmed human cases of swine-origin influenza A (H1N1) infection with known dates of illness onset* --- United States, April 27, 2009

* Onset dates available for 25 of 64 cases.

The above figure shows the number of confirmed human cases of swine-origin influenza A (H1N1) infection with known dates of illness onset in the United States as of April 27, 2009. Onset dates were available for 25 of the 64 confirmed cases.

One case each had onset on March 28 and 30, April 4, 5, 6 and 11. Two cases had onset on April 12. One case had onset on April 15, 19, 20, and 21. Five cases had onset on April 22. Four cases had onset on April 23. Three cases had onset on April 24, and one case had onset on April 25.

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</td></tr></tbody></table> <small>All MMWR HTML versions of articles are electronic conversions from typeset documents. This conversion might result in character translation or format errors in the HTML version. Users are referred to the electronic PDF version (http://www.cdc.gov/mmwr) and/or the original MMWR paper copy for printable versions of official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.</small> **Questions or messages regarding errors in formatting should be addressed to mmwrq@cdc.gov.

Date last reviewed: 4/28/2009

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